This invention relates to plastic film handling and processing equipment, and is more specifically directed to improved plastic film punch equipment for making holes, openings, and/or slits in one or more layers of a plastic film. The invention is more particularly concerned with an improved carrier or holder for a punch head that permits the punch head to be handled safely when storing or transporting the punch head, and when inserting it into or removing it from the punch equipment.
Hole punches and slitter punches are used in bag making machines or the like for punching holes and/or slits in a web of plastic film material. Favorably, a hole punch and a slitter blade are unitarily formed on a base member, to provide a punch unit that can be slid into a quick adapter. The latter typically has a T-slot channel to receive the base of the punch unit with the punch head and slitter blade extending downwards towards a backing plate. The quick adapter is mounted on a rod of a high speed pneumatic cylinder of the punch equipment. The hole punch/slitter punch base unit also has a pair of resilient arms with protruding detents that fit into side recesses in the T-slot channel to hold the punch securely in place in the holder for punching operations. The two resilient arms can be squeezed to disengage the detents from the side recesses and allow the unit to be pulled proximally out of the holder when the punch unit needs to be changed or replaced.
Punch equipment and slitter punches of this type are described in some detail in prior U.S. Pat. No. 6,148,710 to Pottorff, and in prior U.S. Pat. No. 7,080,585 to Prudhomme. The descriptions contained in those two patents are incorporated by reference herein, as background for the types of equipment and punches that provide environment for the safety cover of the present invention.
The cutting edges of the round punch head and associated slitter blade may be quite sharp, and pose a danger to the fingers of the technician when inserting or removing the cutter head into the punching machine. This is also the case for persons carrying the punch units or in packaging or handling them as supply items.
An effective, low-cost but reliable cover was needed that can protect the sharp cutter blade and/or slitter blade from damage in storage or shipment or installation, and can also prevent injury from handling the cutter blade and/or slitter blade when installing the units into the punch equipment and when removing it from the punch equipment.
The equipment that may be associated with which the punch apparatus of this invention may include a bag machine or similar machine in which where the plastic film is prepared for fabrication into bags, protective sleeves, or other plastic film products.
Punches for bag making machines, in which flexible plastic film is cut and/or in which holes or openings are formed in the film, typically have a pneumatic cylinder or other reciprocating device positioned above an apertured backing plate. The web of plastic film is drawn in across the backing plate. The cylinder rod supports a carrier into which the cutting head is placed. The cutting head or punch head may have cutter blades and/or slitter blades of steel, brass, or in some cases plastic. The profile of the cutting head is the shape of the hole that is to be formed in the plastic film. When the film reaches the position where the hole is to be punched, the film transport motion is stopped, and the hole is punched by actuating the air cylinder. A hold-down clamp descends and holds the film in place on the backing plate. The cylinder pushes the head into the film so that it penetrates the film, and enters into an aperture in the backing plate, to cut the desired opening. In the case of a slitter punch, the slitter blade forms a slit at a given position relative to the round opening. Then the head rises back up, the hold-down clamp releases the web of film, and the film moves to the place where the next hole is to be formed. Then the process is repeated. The cut-away circles of plastic film, i.e., “slug”, drop into a waste tube below the apertured backing plate, and can be conducted away, and later recycled or disposed of. The rapid, repeated motion of the round hole punch and the slitter blade into the plastic film will cause wear on the sharp edges of the blade, eventually affecting the performance of the punch and requiring the head to be replaced. Also, when the equipment need to be reconfigured for a different hole punch job, it is usually necessary to remove the punch head, and replace it with a different one with the prescribed hole size and slit size for the subsequent job. Thus there is frequently a need for a technician or other workman to handle these sharp items, remove them from the machine and replace them with a different unit.